Andy Wyenandt

This is an archive of Dr. Wyenandt's posts on the Plant and Pest Advisory.

July 21, 2025 Andy Wyenandt

Diagnosing important diseases in Cucurbit crops – Reference Guide

The following images consist of important diseases in cucurbit crops. These images can be used as a quick reference for diagnosing important fungal and bacterial pathogens. For best results, please turn your device (i.e., cell phone) sideways. For information on commercial control recommendations, please visit the cucurbit sections of the 2024/2025 Mid-Atlantic Commercial Vegetable Production Guide.

Cucurbit powdery mildew (CPM)	Cucurbit powdery mildew	CPM on infected pumpkin stem

Cucurbit downy mildew (CDM)	CDM sporulating on underside of infected cucumber leaf	CDM sporulating on underside of infected cucumber leaf with 10x hand

Anthracnose on cucumber	Anthracnose lesion on infected leaf vein	Anthracnose-infected cucumber fruit

Plectosporium blight on infected stem	Plectosporium lesions on infected vines	Plectosporium lesions on infected pumpkin fruit

Phytophthora blight symptoms	Phytophthora-infected squash	Phytophthora-infected watermelon field

Phytophthora-infected pumpkin	Phytophthora-infected squash fruit	Phytophthora-infected watermelon fruit

Mosaic virus symptoms on leaves of infected pumpkin plant	Pumpkin fruit infected with mosaic virus	Virus infected squash fruit

Fusarium fruit rot of pumpkin	White mold on infected fruit	Gummy stem blight

Choanephora-infected fruit	Choanephora spores in infected pumpkin fruit	Choanephora infecting giant pumpkin fruit

Bacterial wilt infected plant	Symptoms of bacterial canker infected stem	Damage done by cucumber beetle feeding

Angular leaf spot	Shot holes in pumpkin leaves caused by Angular leaf spot in pumpkin	Mature pumpkin fruit with sunscald injury due to the loss of plant canopy

Andy Wyenandt and Kris Holmstrom

Filed Under: Vegetable Crops Tagged With: cucurbit diseases

July 13, 2025 Andy Wyenandt

Diagnosing Southern blight and White mold in tomato and pepper

There have been a few reports of Southern blight (Sclerotinia rolfsii) and White mold (Sclerotinia sclerotiorum) on tomato and pepper in New Jersey. Southern blight is much more common in vegetable areas south of the state where summer temperatures remain hotter (above 90°F) for longer periods of time. Like white mold, it can survive in the soil for many years. Symptoms of Southern blight include infection at the base of the stem at the soil line. The resulting infection will girdle the plant causing wilt and death. The fungus will produce white, cottony mycelium and very small, spherical sclerotia which are often have a tannish, brown color.

White mold is more common than Southern blight in New Jersey, and like Southern blight, once introduced into a field or high tunnel it can very difficult to control. The pathogen produces large black sclerotia on the surface and inside infected stems. If sclerotia of either pathogen make their way back into the soil, both can survive for years causing significant problems.

All infected plants need to be removed immediately and disposed of properly to help reduce the chances of sclerotia returning to the soil.

For more information on chemical control please see the 2024/2025 mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Symptoms of Southern blight on infected pepper plant. Note the numerous, small white to tan colored sclerotia on the stem.

White mold of tomato. Note the large black sclerotia developing inside the brittle stems.

Filed Under: Vegetable Crops Tagged With: pepper, southern blight, tomato, white mold

July 12, 2025 Andy Wyenandt

Diagnosing Verticillium Wilt in Eggplant

Verticillium wilt has been reported in eggplant this summer. It is a common soil-borne fungal pathogen that once it has infested soil can remain for a very long time. Verticillium wilt is caused by either Verticillium albo-atrium or Verticillium dahlia and has a wide host range (over 200 plant species). Both pathogens can survive (overwinter) as microsclerotia in the soil. Verticillium wilt prefers cooler weather and drier soils and can be more severe in neutral to alkaline soils. Solanaceous weeds such as Nightshade may harbor the pathogen. [Read more…]

Filed Under: Vegetable Crops Tagged With: eggplant, verticillium wilt

July 12, 2025 Andy Wyenandt

Controlling phomopsis fruit rot in eggplant

Phomopsis blight is caused by the fungal pathogen, Phomopsis vexans. It survives between seasons in the soil on infested plant debris. Although the pathogen can infect stems and older leaves, fruit infections are most prominent. Cankers that develop on stems and branches can cause the entire plant to collapse and die. Circular, grayish spots may develop on infected leaves. On fruit, the pathogen causes brownish-black spots that can quickly enlarge causing flat spots that can produce black pycnidia (e.g., fruiting bodies) that produce masses of conidia (spores) which are rain dispersed onto healthy plants and fruit. Phomopsis blight is favored by hot, wet weather (85 – 90 F). Spores germinate in free water on leaves and fruit causing infections. The pathogen can survive on solanaceous weeds such as nightshade, so good weed control is necessary. Crop rotations of 3 to 4 years are recommended. If possible, infected fruit should be harvested and removed from the field to help reduce to inoculum and the spread of the disease. Fields should be scouted on a regular basis, especially fields with a history of Phomopsis blight. Fungicide applications include Quadris Top (difenoconazole + azoxystrobin, 7 +11) or Priaxor (fluxapyroxad + pyraclostrobin, 7 +11) rotated with chlorothalonil every 7 to 10 days. For more information please see the 2024/2025 Mid-Atlantic Commercial Vegetable Production Recommendations Guide.

Filed Under: Vegetable Crops Tagged With: eggplant, Fruit Rot, Phomopsis

July 11, 2025 Andy Wyenandt

Cucurbit Downy Mildew Alert – 7/11/25 – Cucumber

Cucurbit downy mildew has been reported on cucumber in Central New Jersey. This is the first report of CDM this growing season in the state. All cucumber and cantaloupe fields need to be scouted on a daily basis and preventative fungicide programs need to be initiated. For more information on CDM and its control please click here.

Filed Under: Vegetable Crops

July 11, 2025 Andy Wyenandt

Preparing for cucurbit downy mildew in 2025

In 2004, cucurbit downy mildew re-emerged in the US with a vengeance causing significant losses in cucurbit production. In most years prior to this, concern for CDM control was minimal, since the pathogen arrived late in the growing season (in more northern regions), or the pathogen caused little damage, or never appeared. After 2004, with significant losses at stake, and with very few fungicides labeled for its proper control, CDM became a serious threat to cucurbit production. Importantly, at the time, cucumber varieties with very good levels of CDM resistance were no longer resistant, suggesting a major shift in the pathogen population. Research done over the past 19 years has led to a better understanding of the pathogen. Recent research has determined that the CDM falls into two separate clades: Clade I and Clade II. [Read more…]

Filed Under: Vegetable Crops Tagged With: cucurbit downy mildew, fungicide resistance management